An image display apparatus for carrying out a three-dimensional image display has been ever used for various purposes such as for games, CAD (Computer Aided Design) systems, aircrafts, or medical devices.
The three-dimensional image can be shown to a user by providing both eyes of the user with object image having an azimuth difference. This is the principle of showing the three-dimensional image to the user. Known are the following typical ways to provide the user with the three-dimensional image.
The first one is the anaglyph principle. According to this principle, the user is provided with a red image for the right eye and a blue image for the left eye, by using an ordinary image display apparatus. In this case, the user should wear an eyeglass provided with blue and red films so that only the red image reaches to the right eye and only the blue image reaches to the left eye, respectively. Thus, the respective eyes of the user can receive only one of the two images corresponding to the respective eyes.
The second one is the polarization eyeglass principle. According to this principle, an image display apparatus for the right eye and an image display apparatus for the left eye are used, and polarization plates, whose planes of polarization are orthogonal to one another, are provided in front of the respective image display apparatuses, so that the images which have passed through the respective polarization plates are combined by a half mirror and directed to the user. In this case, the user should wear an eyeglass provided with polarization plates, whose planes of polarization are orthogonal to one another, so that only the respective images that have passed through the above-described polarization plates can reach to the respective eyes of the user. Thus, the respective eyes of the user can receive only one of the two images corresponding to the respective eyes.
The third one is the time-sharing shutter principle. According to this principle, images having respective azimuth differences are periodically switched and displayed by an ordinary image display apparatus. In this case, the user should wear an eyeglass whose shutters for the respective right and left eyes are alternately and periodically closed. The closing of the shutters and the switching of the images are carried out in synchronization with each other, so that the respective eyes of the user can receive only one of the two images corresponding to the respective eyes.
The fourth one is the parallax barrier principle. This principle is disclosed in U.S. Pat. No. 6,392,690 (issued on May 21, 2002), for example. The following description deals with this principle with reference to FIGS. 19 and 20.
According to this principle, a three-dimensional image display apparatus 150 is arranged such that (a) a display device such as a liquid crystal display device 151 is sandwiched by upper and lower linear polarization plates 162 and 163, and (b) a parallax barrier 171 is further provided in front of a display screen of the liquid crystal display device 151. The liquid crystal display device 151 includes pixel groups 164 each made of n pixels. The pixels in the pixel groups 164 are disposed as follows.
More specifically, they are disposed like (R1, G2, B3, . . . , Rn), (G1, B2, R3, . . . , Gn), (B1, R2, R3, . . . , Bn), and so on. Note that (a) the pixels in the same parentheses are assumed to belong to the same pixel group 164, (b) the R, G, and B indicate pixels that are driven in response to color signals corresponding to red, green, and blue colors, respectively, and (c) each subscript number indicates one of the n azimuth difference images. Thus, in the liquid crystal display device 151, the respective pixels displaying the azimuth difference images are arranged R, G, and B in this order.
Note that the n azimuth difference images indicate n images which are obtained by viewing an object from 1 through n directions, respectively. The principle of using n images is generally referred to as n-eye type.
The parallax barrier 171 includes a plurality of slits each functioning as an opening section 172, and light shielding sections 173, as shown in FIG. 19. In the three-dimensional image display apparatus 150, the pixel groups 164 and the opening sections 172 are provided such that one pixel group 164 in the liquid crystal display device 151 corresponds to one opening section 172.
With the arrangement, the outgoing light from the respective pixels in the liquid crystal display device 151 is fundamentally directed in all directions. The outgoing light from the pixels belonging to a same pixel group 164 passes through a same opening section 172 as shown by optical paths indicated by arrows in FIG. 19.
This allows that observation regions E1 through En in which “1” through “an” images can be observed, respectively, are formed in a space-division manner in front of the three-dimensional image display apparatus 150 (see FIG. 20). For example, when a user put his or her eyes in the observation region E1, the user can entirely observe “1” image displayed by the liquid crystal display device 151. Accordingly, when a user, on an opposite side of the liquid crystal display device 151 with respect to the parallax barrier 171, puts his or her respective eyes in any two observation regions among the observation regions E1 through En, the user can select one of the “1” through “n” images so as to observe the three-dimensional image. In other words, the user can observe various three-dimensional images in accordance with an angle in which the user views.
The fifth one is the lenticular lens principle. This principle is disclosed in the foregoing U.S. Pat. No. 6,392,690, for example. The following description deals with this principle with reference to FIG. 21.
According to this principle, a three-dimensional image display apparatus 150 is arranged such that the parallax barrier 171 is replaced with a lenticular lens 181 that is provided in front of the display screen of the liquid crystal display device 151.
The lenticular lens 181 is arranged such that a plurality of cylindrical lenses 182 are aligned on a substrate 183, and such that one pixel group 164 of the liquid crystal display device 151 corresponds to one cylindrical lens 182. When a user observes the display screen via the lenticular lens 181, an image which the user can observe is selected by the cylindrical lens 182 in accordance with an angle in which the user views.
For example, when a user is in a direction (in a direction indicated as a solid arrow in FIG. 21) where the outgoing light from a pixel (hereinafter referred to as pixel 1) that displays an image of an object viewed from a direction “1” passes through a principal point of the cylindrical lens 182, the user can observe only the image of the pixel 1 shown by a region indicated as two broken lines. Thus, when the lenticular lens 181 is provided in front of the liquid crystal display device 151, the effects similar to those of the case where the parallax barrier 171 is provided are obtained.
As described above, the U.S. Pat. No. 6,392,690 discloses a technique for carrying out the three-dimensional image display, however, does never consider a technique for switching a three-dimensional image and a two-dimensional image and for displaying the image thus switched.